To test electronic circuits produced on wafers, for example for their ability to operate and their electrical characteristics, use is usually made of measuring probes which are applied mechanically to appropriate contact points on the electronic circuit to be tested. Electronic circuits of this kind which need to be tested are increasingly circuits which generate or process high-frequency signals, which means that for the measuring probe there is an impedance of which due note needs to be taken. In other words, the measuring probe needs to have an impedance matched to the contact with the electrical circuit to be tested as otherwise, if there are mismatches, there will, as is generally known, be corresponding reflections which will have an unwanted effect on any measurement made or will make measurement totally impossible. There should not even be any change in impedance over the measuring probe itself because changes in impedance of this kind also cause corresponding points of reflection.
Hence there is known from U.S. Pat. No. 4,697,143 a measuring probe which, to allow a constant impedance to be obtained from a measuring cable to a contact point, has a co-planar conductor structure, with a signal conductor and a ground conductor being spaced away from one another in such as a way as to produce a desired constant impedance. However, this arrangement has the disadvantage that, due to the use of an aluminium oxide substrate, complicated shielding is required to avoid higher-order modes. Also, the measuring probe is complicated, laborious and cost-intensive to produce. Because of the relevant tolerances, not every measuring probe produced meets the preset parameters and for this reason there is a high scrap rate in production, which makes the measuring probe even more expensive. In addition, the totally rigid arrangement of the co-planar conductor structure having three or more conductors means there is a problem in making contact. This is because, given the dimensions that exist on wafers and the corresponding tolerances to which the measuring probe, the contact points and the mechanical alignment of the measuring probe are subject, it is virtually impossible mechanically for all the conductors in the measuring probe's co-planar conductor structure to be precisely in the plane of the contact points when the probe is applied to the points. Hence certain conductors contact their particular contact point better and others contact theirs less satisfactorily or not at all.
From U.S. Pat. No. 4,894,612 is known a measuring probe in which a dielectric is arranged over a complete length of a co-planar conductor structure. What is further disclosed is a measuring probe having strip lines where ends of the strip lines stand out resiliently from a substrate acting as a mounting.
The object of the invention is therefore to provide an improved measuring probe of the above kind, with simple and inexpensive volume production being achieved in this case with, at the same time, contact of a good standard.